Sheet post-finishing apparatuses are extensively used, which stack the sheets sent from the image forming apparatus to form bundle of sheets, and which conducts a saddle stitching process onto the bundle of sheets to generate a booklet.
Among various technologies having been applied onto the stitching process, most well-known is a technology to stitch the bundle of sheets by a stapling device.
A saddle stitching process represents a process to stitch the bundle of sheets with staples at a predetermined central position in the long direction of the bundle of sheets where each sheet is to be divided into two equal portions.
The sheet post-finishing apparatuses to conduct said saddle stitching process are mostly premised to be combined to the image forming apparatus, and used as an image forming system (See Unexamined Japanese Patent Application Publication No. H8-192,951).
The stapling device used in the saddle stitching process cannot be placed at the edge portion of the sheets to be stacked, though the stapling device used in a stitching process to staple the edge portion of the sheets can be placed.
Accordingly, the stapling device is configured in such a way that before the bundle of sheets is formed, the stapling device stays away to a position where the stapling device does not interfere with the sheet stacking operation, such as a position at the edge of the sheets to be stacked along the long edge, and after the bundle of sheets has been formed, the stapling device returns to its functional position, and conducts the stapling operation.
In order to conduct a correct stitching process, the leading portion and both end portions of the bundle of sheets stacked on a sheet stacking section must be neatly aligned.
However, as described above, since the stapling device is configured to move along the surface of the bundle of sheets, it is very difficult to provide guide members to restrict both surfaces of the sheet being conveyed toward the sheet stacking device, at the desired position.
Specifically, in case of a stapling process in which a single stapling device is sequentially moved to staple the bundle of sheets at plural portions (see Unexamined Japanese Patent Application Publication No. 2003-334,803), the stapling device moves over a large area, so that the guide member is barely provided at the desired position.
As a result, the sheet is unstably conveyed into the sheet stacking section, whereby the edges of the sheets being stacked on the sheet stacking section are not properly aligned, which is an adverse matter.
Accordingly, a guide member, to restrict both surfaces of the sheet being conveyed into the sheet stacking section, is necessarily provided to face a center surface of the sheet. When said stapling device is moved, a driving mechanism is necessarily provided to move said guide member, so that the movement of the stapling member is not disturbed.
However such a driving mechanism may result in a price increase of the apparatus.